Ecological dynamics
The Upland Stony Loam (Wyoming sagebrush) South site is found in the Great Salt Lake Area of the Basin and Range Ecological Provence. It developed under the natural ecological conditions found there, including the normal influences of native wildlife herbivory, fire and climate. Wyoming big sagebrush dominates the shrub layer. A mix of other shrubs including antelope bitterbrush, black sagebrush, and Utah serviceberry are commonly found. Perennial herbaceous species occurrence and production is directly related to overstory canopy density with bluebunch wheatgrass, Nevada bluegrass, and Indian ricegrass found most often.
This site is vulnerable to an increase in both pinyon and juniper trees without disturbances that keep the tree densities lower (i.e. fire). Singleleaf pinyon and Utah juniper may dominate the site if there is time without disturbances and eventually out-compete mountain big sagebrush for water and sunlight, severely reducing both the shrub and herbaceous understory (Miller et al. 2000, Lett and Knapp 2005). Bluegrasses may remain underneath trees on north-facing slopes. The potential for soil erosion increases as the Utah juniper woodland matures and the understory plant community cover declines (Pierson et al. 2010).
Cheatgrass and annual forbs are most likely to invade this site.
As vegetative communities respond to changes that cause them to cross ecological thresholds, a return to previous states may not be possible. The amount of effort needed to affect desired vegetative shifts depends on the present biotic and abiotic features and the desired results.
Fire Ecology:
Infilling by younger trees increases canopy cover causing a decrease in understory perennial vegetation and an increase in bare ground. As pinyon and juniper trees increase in density so has their litter. Phenolic compounds of juniper scales can have an inhibitory effect on grass growth (Jameson 1970). Furthermore, infilling shifts stand level biomass from ground fuels to canopy fuels which has the potential to significantly impact fire behavior. The more tree dominated pinyon and juniper woodlands become, the less likely they are to burn under moderate conditions, resulting in infrequent high intensity fires (Gruell 1999, Miller et al. 2008). Additionally, as the understory vegetation declines in vigor and density with increased canopy the seed and propagules of the understory plant community also decrease significantly. The increase in bare ground allows for the invasion of non-native annual species such as cheatgrass and with intensive wildfire the potential for conversion to annual exotics is a serious threat (Tausch 1999, Miller et al. 2008). The introduction of annual weedy species, like cheatgrass, may cause an increase in fire frequency and eventually lead to an annual dominated community (Miller et al. 2013). Infilling by singleleaf pinyon and Utah juniper may also occur with an extended fire return interval. Without fire or changes in management, pinyon and juniper will dominate the site and Wyoming big sagebrush will be severely reduced. The herbaceous understory will typically be reduced. The potential for soil erosion increases as the juniper woodland matures and the understory plant community cover declines. Catastrophic wildfire in juniper controlled sites may lead to an annual weed dominated site.
Livestock/Wildlife Grazing Interpretations:
Overgrazing leads to an increase in sagebrush and a decline in understory plants like bluebunch wheatgrass. Squirreltail will increase temporarily with further degradation. Invasion of annual weedy forbs and cheatgrass could occur with further grazing degradation, leading to a decline in squirreltail and an increase in bare ground. Wetter sites are more resistant to degradation and may end up having sagebrush and Sandberg bluegrass dominate the site. A combination of overgrazing and prolonged drought may lead to soil redistribution, increased bare ground and a loss in plant production. Bluebunch wheatgrass is moderately grazing tolerant but is very sensitive to defoliation during the active growth period (Blaisdell and Pechanec 1949, Laycock 1967, Anderson and Scherzinger 1975). Sandberg bluegrass may slow reestablishment of deeper rooted bunchgrass, increase under grazing pressure (Tisdale and Hironaka 1981) and is capable of co-existing with cheatgrass. Reduced bunchgrass vigor or density provides an opportunity for Sandberg bluegrass expansion and/or cheatgrass and other invasive species to occupy interspaces, leading to increased fire frequency and potentially an annual plant community. Depending on the season of use, the grazer and site conditions, either Sandberg bluegrass or cheatgrass may become the dominant understory with inappropriate grazing management. For example, Daubenmire (1970) found that heavy sheep grazing favors Sandberg bluegrass, while heavy cattle grazing favors cheatgrass.
These plant communities may not represent every possibility, but they are the most prevalent and repeatable plant communities. As more data is collected, some of these plant communities may be revised or removed and new ones may be added. None of these plant communities should necessarily be thought of as the “desired plant community”. According to the USDA NRCS National Range and Pasture Handbook, the desired plant community will be determined by the decision makers and will meet minimum quality criteria established by the NRCS. The main purpose for including any description of a plant community here is to capture the current knowledge and experience at the time of this revision.
Six possible alternative stable states have been hypothesized for this ecological site. The Reference State contains four community phases, shrub/grass dominated, shrub dominated, grass dominated, and a fire tolerant phase. The primary drivers in this state are fire, drought, and/or insect of disease. The Current Potential State is like the Reference State; however, non-native species have been introduced in the system which alters the resilience and resistance of the state. The Tree State occurs when there has been sufficient time for junipers and/or pinyon trees to increase in density and dominate the site dynamics. The Annual State occurs after large fires or multiple fires that promote annual invasive species dominance over native shrubs and grasses. The seeded state occurs after seeding has been implemented and can occur potentially from any state. Specific community phases and transitions will be described in the narratives below.
State 1
Reference State
The Reference State includes the plant communities that were best adapted to the unique combination of factors associated with the ecological site. It was in a natural dynamic equilibrium with the historic biotic, abiotic, and climatic factors on its ecological site in North America at the time of European immigration and settlement. This dominant aspect of the plant community is Wyoming big sagebrush and bluebunch wheatgrass. The community production by dry weight is 50 percent grass, 10 percent forbs, and 40 percent shrubs.
Community 1.1
Wyoming big sagebrush/perennial bunchgrasses
This community is dominated by big sagebrush and bluebunch wheatgrass. Forbs and other grasses make up smaller components. The composition by air-dry weight is approximately 50 percent perennial grasses, 10 percent forbs, and 40 percent shrubs.
Table 5. Annual production by plant type
| Plant type |
Low
(lb/acre) |
Representative value
(lb/acre) |
High
(lb/acre) |
| Grass/Grasslike |
200 |
425 |
750 |
| Shrub/Vine |
160 |
340 |
600 |
| Forb |
40 |
85 |
150 |
| Total |
400 |
850 |
1500 |
Table 6. Ground cover
| Tree foliar cover |
0%
|
| Shrub/vine/liana foliar cover |
10-20%
|
| Grass/grasslike foliar cover |
15-35%
|
| Forb foliar cover |
3-5%
|
| Non-vascular plants |
0%
|
| Biological crusts |
0%
|
| Litter |
0%
|
| Surface fragments >0.25" and <=3" |
0%
|
| Surface fragments >3" |
0%
|
| Bedrock |
0%
|
| Water |
0%
|
| Bare ground |
0%
|
Table 7. Canopy structure (% cover)
| Height Above Ground (ft) |
Tree |
Shrub/Vine |
Grass/
Grasslike |
Forb |
| <0.5 |
– |
– |
– |
– |
| >0.5 <= 1 |
– |
– |
– |
0-10% |
| >1 <= 2 |
– |
– |
30-40% |
– |
| >2 <= 4.5 |
– |
15-25% |
– |
– |
| >4.5 <= 13 |
– |
– |
– |
– |
| >13 <= 40 |
– |
– |
– |
– |
| >40 <= 80 |
– |
– |
– |
– |
| >80 <= 120 |
– |
– |
– |
– |
| >120 |
– |
– |
– |
– |
| Jan |
Feb |
Mar |
Apr |
May |
Jun |
Jul |
Aug |
Sep |
Oct |
Nov |
Dec |
| J |
F |
M |
A |
M |
J |
J |
A |
S |
O |
N |
D |
Community 1.2
Perennial bunchgrasses/fire-tolerant shrubs
This community phase is characteristic of a post-disturbance, early-seral community. Bluebunch wheatgrass and other perennial bunchgrasses dominate. Depending on fire severity or intensity, patches of intact sagebrush may remain.
Community 1.3
Perennial grasses/Wyoming big sagebrush
Big sagebrush begins to increase in the absence of disturbance or with grazing management that favors shrubs. Decadent sagebrush dominates the overstory and the deep-rooted perennial bunchgrasses in the understory are reduced either from competition with shrubs or from grazing management. Utah juniper and/or singleleaf pinyon may be present.
Community 1.4
Wyoming big sagebrush/perennial bunchgrasses/Utah juniper-pinyon
Big sagebrush increases in the absence of disturbance or with grazing management that favors shrubs. Decadent sagebrush dominates the overstory and the deep-rooted perennial bunchgrasses in the understory are reduced either from competition with shrubs or from grazing management. Utah juniper and/or singleleaf pinyon may be present.
Pathway 1.1a
Community 1.1 to 1.2
Fire will decrease or eliminate the overstory of sagebrush and allow for the perennial bunchgrasses to dominate the site. Fires will typically be low severity resulting in a mosaic pattern due to low fuel loads. A fire following an unusually wet spring may be more severe and reduce sagebrush cover to trace amounts. Coupled with drought conditions, a severe infestation of Aroga moth could also reduce sagebrush within the community, giving a competitive advantage to the perennial grasses and forbs. This phenomenon is more likely at the lower end of the precipitation range.
Pathway 1.1b
Community 1.1 to 1.4
Long term drought may reduce fire frequency and increase shrub cover, time and/or inappropriate grazing management may also favor an increase in big sagebrush over deep-rooted perennial bunchgrasses. Combinations of these would allow the sagebrush overstory to increase and dominate the site, causing a reduction in the perennial bunchgrasses. Sandberg bluegrass may increase in density depending on the grazing management.
Pathway 1.2a
Community 1.2 to 1.1
Time and lack of disturbance will allow sagebrush to increase.
Pathway 1.2b
Community 1.2 to 1.3
Time and lack of disturbance such as fire or drought. Inappropriate grazing management may also decrease perennial understory.
Pathway 1.3a
Community 1.3 to 1.1
A low severity fire will reduce the sagebrush overstory and create a sagebrush/grass mosaic. Coupled with drought, Aroga moth infestation may reduce sagebrush dominance and allow recovery of the perennial bunchgrass understory.
Pathway 1.3b
Community 1.3 to 1.2
Fire will decrease or eliminate the overstory of sagebrush and allow for the perennial bunchgrasses to dominate the site. Fires will typically be low severity, resulting in a mosaic pattern due to low fine fuel loads. A fire following an unusually wet spring or a change in management favoring an increase in fine fuels may be more severe and reduce sagebrush cover to trace amounts.
Pathway 1.4a
Community 1.4 to 1.2
Fire reduces shrub cover returning the community to a grass dominated phase.
State 2
Current Potential State
The Current Potential State is like the Reference State 1 with similar community phases. Ecological function has not changed; however, the resiliency of the state has been reduced by the presence of invasive weeds. Non-natives may increase in abundance but will not become dominant within this state. These non-natives can be highly flammable and can promote fire where historically fire had been infrequent. Negative feedbacks enhance ecosystem resilience and contribute to the stability of the state. These feedbacks include the presence of all structural and functional groups, low fine fuel loads, and retention of organic matter and nutrients. Positive feedbacks decrease ecosystem resilience and stability of the state. These include the nonnatives’ high seed output, persistent seed bank, rapid growth rate, ability to cross pollinate, and adaptations for seed dispersal. Additionally, the presence of highly flammable, non-native species reduces State resilience because these species can promote fire where historically fire has been infrequent leading to positive feedbacks that further the degradation of the system.
Community 2.1
Wyoming big sagebrush/perennial bunchgrass/non-native species
This community phase is similar to the Reference State Community Phase 1.1, with the presence of non-native species in trace amounts. Sagebrush, bluebunch wheatgrass, and Indian ricegrass dominate the site. Forbs and other shrubs and grasses make up smaller components of the plant community.
Community 2.2
Perennial bunchgrasses/fire-tolerant shrubs/annual non-native species
This community phase is characteristic of a post-disturbance; early seral community where annual non-native species are present. Sagebrush is present in trace amounts; perennial bunchgrasses dominate the site. Depending on fire severity patches of intact sagebrush may remain. Rabbitbrush may be sprouting. Perennial forbs may be a significant component for several years following fire. Annual non-native species are stable or increasing within the community.
Community 2.3
Perennial bunchgrasses/native shrubs/non-native species
This community is at risk of crossing a threshold to another state. Sagebrush dominates the overstory and perennial bunchgrasses in the understory are reduced from competition with shrubs, inappropriate grazing, or both. Rabbitbrush may be a significant component. Sandberg bluegrass may increase and become co-dominant with deep rooted bunchgrasses. Annual nonnatives species may be stable or increasing due to lack of competition with perennial bunchgrasses. This site is susceptible to further degradation from grazing, drought, and fire.
Community 2.4
Wyoming big sagebrush/perennial bunchgrasses/non-native species/Utah juniper (at-risk)
This community is at risk of crossing into an annual state. Native bunchgrasses dominate; however annual non-native species such as cheatgrass may be sub-dominant in the understory. Annual production and abundance of these annuals may increase drastically in years with heavy spring precipitation. Seeded species may be present. Sagebrush and/or bitterbrush are a minor component. Utah juniper and singleleaf pinyon may be present and without management will likely increase. This site is susceptible to further degradation from grazing, drought, and fire.
Pathway 2.1a
Community 2.1 to 2.2
Fire reduces the shrub overstory and allows for perennial bunchgrasses to dominate the site. Fires are typically low severity resulting in a mosaic pattern due to low fuel loads. A fire following an unusually wet spring or a change in management favoring an increase in fine fuels may be more severe and reduce sagebrush cover to trace amounts. Annual non-native species are likely to increase after fire. Aroga moth infestations can also cause mortality of the big sagebrush overstory.
Pathway 2.1b
Community 2.1 to 2.4
Time and lack of disturbance allows for sagebrush to increase and become decadent. Long term drought reduces fine fuels and leads to a reduced fire frequency, allowing big sagebrush to dominate the site. Inappropriate grazing management reduces the perennial bunchgrass understory; conversely Sandberg bluegrass may increase in the understory depending on grazing management.
Pathway 2.2a
Community 2.2 to 2.1
Time and lack of disturbance and/or grazing management that favors the establishment and growth of sagebrush allows the shrub component to recover. The establishment of big sagebrush can take many years.
Pathway 2.2b
Community 2.2 to 2.3
Tree/shrub removal treatment or prescribed burning in the presence of annual grass species will reduce shrub canopy may cause a shift to Phase 2.3. A subsequent year with precipitation that is favorable to nonnative annual grasses may speed up this pathway.
Pathway 2.3a
Community 2.3 to 2.1
A change in grazing management that reduces shrubs will allow for the perennial bunchgrasses in the understory to increase. Heavy late-fall/winter grazing may cause mechanical damage and subsequent death to sagebrush, facilitating an increase in the herbaceous understory. Brush treatments with minimal soil disturbance will also decrease sagebrush and release the perennial understory. Annual non-native species are present and may increase in this community.
Pathway 2.3b
Community 2.3 to 2.2
Fire reduces or eliminates the overstory of sagebrush and allows for the understory perennial grasses to increase. Fires will typically be low severity resulting in a mosaic pattern due to low fine fuel loads. Following an unusually wet spring or a change in management favoring an increase in fine fuels, a fire may be more severe and reduce the shrub component to trace amounts. Annual non-native species respond well to fire and may increase post-burn.
Pathway 2.4a
Community 2.4 to 2.2
Fire reduces or eliminates the overstory of sagebrush and allows for the understory perennial grasses to increase. Fires will typically be low severity resulting in a mosaic pattern due to low fine fuel loads.
State 3
Shrub State
The Shrub State has two community phases and is the product of many years of heavy grazing during time periods harmful to deep-rooted perennial bunchgrasses. With a reduction in deep-rooted perennial bunchgrass competition, bluegrasses, and squirreltail will increase and become the dominant grass. Sagebrush dominates the overstory. Bitterbrush and/or rabbitbrush may be significant components. Sagebrush cover exceeds site concept and may be decadent, reflecting stand maturity and lack of seedling establishment due to competition with mature plants. Bare ground is also increasing. The shrub overstory and bluegrass understory dominate site resources such that soil water, nutrient capture, nutrient cycling, and soil organic matter are temporally and spatially redistributed.
Community 3.1
Wyoming big sagebrush/non-native annual grass
This phase is at risk of transitioning to another state. Wyoming big sagebrush, possibly decadent, dominates overstory and rabbitbrush may be a significant component. Deep-rooted perennial bunchgrasses may be present in trace amounts or absent from the community. Sandberg bluegrass, squirreltail, and annual non-native species increase. Understory may be sparse, with bare ground increasing. Utah juniper or singleleaf pinyon may be present because of encroachment from neighboring sites and lack of disturbance.
Community 3.2
Wyoming big sagebrush/sparse understory
This phase occurs after drought that reduces annual grass cover or after inappropriate grazing management.
Pathway 3.1a
Community 3.1 to 3.2
Time and lack of disturbance may be coupled with inappropriate grazing management.
Pathway 3.2a
Community 3.2 to 3.1
Low severity fire or aroga moth infestation creates reduced big sagebrush cover. This pathway could also occur with brush management.
State 4
Tree State
The Tree State has two community phases that are characterized by the dominance of Utah juniper and singleleaf pinyon in the overstory. This state is identifiable by 30 to over 50 percent cover of Utah juniper and singleleaf pinyon. This stand exhibits a mixed age class. Older trees are at maximal height and upper crowns may be flat-topped or rounded. Younger trees are typically cone- or pyramidal shaped. Understory vegetation is sparse due to increasing shade and competition from trees.
Community 4.1
Utah juniper/big sagebrush/non-native annual grass
Singleleaf pinyon and Utah juniper dominate the aspect. Understory vegetation is thinning. Perennial bunchgrasses are sparse and big sagebrush skeletons are as common as live shrubs due to tree competition for soil water, overstory shading, and duff accumulation. Tree canopy cover is greater than 30 percent. Annual non-native species are present or co-dominate in the understory. Bare ground areas are prevalent. This community phase is typically described as a Phase II woodland (Miller et al. 2008).
Community 4.2
Utah juniper/sparse understory
Singleleaf pinyon and Utah juniper dominate the aspect. Tree canopy cover exceeds 30 percent and may be as high as 50 percent. Understory vegetation is sparse to absent. Perennial bunchgrasses, if present, exist in the dripline or under the canopy of trees. Sagebrush skeletons may be present or absent. Mat-forming forbs or Sandberg’s bluegrass may dominate interspaces. Annual nonnative species are present and are typically found under the trees. Bare ground areas are large and interconnected. Soil redistribution may be extensive. This community phase is typically described as a Phase III woodland (Miller et al. 2008 ).
Pathway 4.1a
Community 4.1 to 4.2
Time without disturbance such as fire, long-term drought, or disease will allow for the gradual maturation of singleleaf pinyon and Utah juniper. Infilling by younger trees continues.
Pathway 4.2a
Community 4.2 to 4.1
Stand thinning treatment.
State 5
Annual State
The Annual State is characterized by the dominance of annual non-native species such as cheatgrass and tansy mustard in the understory. Rabbitbrush may dominate the overstory. Annual non-native species dominate the understory.
Community 5.1
Non-native annual species/native shrubs
Rabbitbrush is typically the dominant overstory shrub. Sagebrush may be a significant component. Annual non-native plants such as tansy mustard and cheatgrass dominate the understory.
Community 5.2
Non-native annual species
Cheatgrass, mustards and other non-native annual species dominate the site. Trace amounts of perennial bunchgrasses may be present.
Pathway 5.1a
Community 5.1 to 5.2
Fire reduces or eliminates the overstory shrub component and allows for annual non-native species to dominate the phase.
Pathway 5.2a
Community 5.2 to 5.1
Time and lack of fire allows for sagebrush/rabbitbrush to establish. Probability of sagebrush establishment is dependent on a near-by seed source from unburned patches of sagebrush.
State 6
Seeded State
The Seeded State has two community phases a grass-dominated phase and a grass-shrub phase. The state is characterized by the dominance of seeded species such as smooth brome and crested wheatgrass. Other seeded species include forage kochia, Wyoming big sagebrush, and native and non-native perennial forbs.
Community 6.1
Seeded species/native shrubs/non-native annuals
Introduced grass species and other non-native species such as forage kochia dominate the community. Native and non-native seeded forbs may be present. Trace amounts of big sagebrush may be present, especially if seeded. Annual non-native species present.
Community 6.2
Big sagebrush/seeded species/non-native annuals
This community phase is at risk of crossing a threshold and transitioning to another state. Wyoming sagebrush dominates. Rabbitbrush may be a significant component. Seeded grass vigor and density are reduced. Annual non-native species stable to increasing. Utah juniper and/or singleleaf pinyon may be present. This site is susceptible to further degradation from grazing, drought, and fire.
Pathway 6.1a
Community 6.1 to 6.2
Inappropriate grazing management, particularly during the growing season, reduces perennial bunchgrass vigor and density and facilitates shrub establishment.
Pathway 6.2a
Community 6.2 to 6.1
Fire eliminates/reduces the overstory of sagebrush and allows for the understory perennial grasses to increase. Fires will typically be low severity resulting in a mosaic pattern due to low fine fuel loads. A fire following an unusually wet spring or change in management favoring an increase in fine fuels, may be more severe and reduce the shrub component to trace amounts. A severe infestation of Aroga moth will also cause a large decrease in sagebrush within the community, giving a competitive advantage to the perennial grasses and forbs. Brush treatments with minimal soil disturbance will also decrease sagebrush and release the perennial understory. Annual non-native species respond well to fire and may increase post-burn.
Transition T1A
State 1 to 2
Trigger: This transition is caused by the introduction of non-native annual plants, such as cheatgrass, mustards, and bur buttercup.
Slow variables: Over time the annual non-native species will increase within the community.
Threshold: Any amount of introduced non-native species causes an immediate decrease in the resilience of the site. Annual non-native species cannot be easily removed from the system and have the potential to significantly alter disturbance regimes from their historic range of variation.
Transition T2A
State 2 to 3
Trigger: To Community Phase 3.1: Repeated heavy growing season grazing will decrease or eliminate deep rooted perennial bunchgrasses, increase Sandberg bluegrass and favor shrub growth and establishment.
Slow variables: Long term decrease in deep-rooted perennial grass density.
Threshold: Loss of deep-rooted perennial bunchgrasses changes nutrient cycling, nutrient
redistribution, and reduces soil organic matter.
Transition T2B
State 2 to 4
Trigger: Time and lack of disturbance or management action allows for Utah Juniper and singleleaf pinyon to dominate. This may be coupled with grazing management that favors tree establishment by reducing understory herbaceous competition for site resources
Slow variables: Over time the abundance and size of trees will increase.
Threshold: Trees dominate ecological processes and number of shrub skeletons exceed number of live shrubs.
Transition T2C
State 2 to 5
Trigger: Fire and/or multiple fires lead to plant community phase 5.1, inappropriate grazing management that favors shrubs in the presence of non-native annual species leads to community phase 5.2.
Slow variables: Increased production and cover of non-native annual species.
Threshold: Loss of deep-rooted perennial bunchgrasses and shrubs truncates, spatially and temporally, nutrient capture and cycling within the community. Increased, continuous fine fuels from annual non-native plants modify the fire regime by changing intensity, size and spatial variability of fires.
Restoration pathway R3A
State 3 to 2
Brush management such as mowing, coupled with seeding of deep-rooted native bunchgrasses will reduce the shrub overstory and release the perennial understory species. Presence of annual nonnative species increases the risk of transitioning to an annual state if this treatment fails.
Transition T3A
State 3 to 4
Trigger: Time and a lack of disturbance or management action allows for Utah Juniper and singleleaf pinyon to dominate site. This may be coupled with grazing management that favors tree establishment by reducing understory herbaceous competition for site resources.
Slow variables: Over time the abundance and size of trees will increase.
Threshold: Trees overtop mountain sagebrush and out-compete shrubs for water and sunlight.
Shrub skeletons exceed live shrubs with minimal recruitment of new cohorts.
Transition T3B
State 3 to 5
Trigger: To Community Phase 5.1: Severe fire. To Community Phase 5.2: Inappropriate grazing management in the presence of annual non-native species.
Slow variables: Increased production and cover of non-native annual species.
Threshold: Increased continuous fine fuels modify the fire regime by changing intensity, size, and spatial variability of fires. Changes in plant community composition and spatial variability of vegetation due to the loss of perennial bunchgrasses and sagebrush truncate energy capture spatially and temporally thus impacting nutrient cycling and distribution.
Restoration pathway R4A
State 4 to 2
Tree removal and seeding of desired species. Tree removal practices that minimize soil disturbance are recommended. Probability of success declines with increased presence of nonnative annual species (Community Phase 4.2).
Restoration pathway R4B
State 4 to 3
This restoration is recommended for phase 4.1 only due to the lack of understory in 4.2. Removal of the pinyon and juniper overstory through tree removal practices or a controlled burn, without seeding of grass species, would move this phase into a shrub state. If nonnative annuals are present, a controlled burn is not recommended.
Transition T4A
State 4 to 5
Trigger: Fire reduces the tree overstory and allows for the annual non-native species in the understory to dominate the site. Soil disturbing treatments such as slash and burn may also reduce tree canopy and allow for non-native annual species to increase.
Slow variables: Over time, cover and production of annual non-native species increases.
Threshold: Loss of deep-rooted perennial bunchgrasses and shrubs changes temporal and spatial nutrient capture and cycling within the community. Increased, continuous fine fuels modify the fire regime by increasing frequency, size, and spatial variability of fires.
Transition T4B
State 4 to 6
Tree removal and seeding of desired species. Tree removal practices that minimize soil disturbance are recommended. Probability of success declines with increased presence of nonnative annual species (Community Phase 4.2).
Transition T5A
State 5 to 6
Seeding of deep-rooted bunchgrasses, coupled with brush management and/or herbicide. Probability of success is medium.
Transition T6A
State 6 to 4
Trigger: Time and lack of disturbance or management action allows for Utah Juniper to dominate. This may be coupled with grazing management that favors tree establishment by reducing understory herbaceous competition for site resources
Slow variables: Over time, the abundance and size of trees will increase.
Threshold: Trees dominate ecological processes and number of shrub skeletons exceed number of live shrubs.
Transition T6B
State 6 to 5
Trigger: Catastrophic fire.
Slow variables: Increased production and cover of non-native annual species.
Threshold: Increased continuous fine fuels modify the fire regime by changing intensity, size, and spatial variability of fires. Changes in plant community composition and spatial variability of vegetation due to the loss of perennial bunchgrasses and sagebrush truncate energy capture spatially and temporally, thus impacting nutrient cycling and distribution.
